The present invention relates to an optical disc and an optical disc apparatus for using the same.
An optical disc is a medium on which data can be recorded at a high density. Data are recorded by radiating the disc with a laser beam. An optical disc apparatus records data on such a disc and reads the recorded data from the disc. The optical disc and the optical disc apparatus are used for recording and reading a great amount of video data.
Optical discs are shipped from the factory with no data recorded on them. They each have tracking pregrooves and prepits--all cut in a recording layer. The prepits present the serial numbers of tracks. Data are recorded on the disc in the following way.
The optical disc is rotated. While the disc is rotating, an optical head is moved in the radial direction of the disc until it reaches a desired tracking pregroove. The optical head therefore traces the tracking pregroove. Data are supplied to the optical head. The optical head emits a recording laser beam which is modulated according to the data. As the beam is radiated on the disc, data pits corresponding to the data are cut in the recording layer of the disc. At the same time, clock pits are cut in the recording layer.
The recorded data are read in the following way. The disc is rotated, and the optical head is moved in the radial direction of the disc until it reaches the tracking pregroove. A reading laser beam is then emitted while the optical head is tracing the pregroove. The data pits and the clock pits made in the recording layer are scanned with the laser beam, thereby reading the data from the optical disc.
With the conventional optical disc and the apparatus both mentioned above it is necessary to cut tracking pregrooves and clock pits. This limits that area of the recording layer in which data pits may be cut. It follows that the recording density is limited. Further, since the pregrooves have a depth and a width and the prepits have another depth and another width, the process of cutting them is rather complicated.